1. Field of the Invention
This invention relates to reducing the phytotoxicity of conventional horticultural petroleum spray oils by incorporation in such oils of zinc dialkyldithiophosphates.
Petroleum oils are used in agriculture as carriers or solvents for spraying pesticides (fungicides, insecticides, ovicides, etc.), herbicides, micronutrients and various types of chemical adjuvants. They are also used as agricultural spray oils in their own right, i.e., without additives, because of their natural herbicidal and pesticidal properties. They control a wide range of pests, for examples, Sigatoka disease in banana, earworm in sweet corn, Cercospora in sugar beet, and mites, aphids, scale insects in deciduous fruit trees, citrus and ornamentals. The main advantages of petroleum spray oils are their relative cheapness, their low health hazard and the apparent inability of fungi, insects and mites to develop strains resistant to them.
The properties required for an oil to perform efficiently as a carrier do not necessarily conflict with those required for an oil to act as a natural herbicidal or pesticidal spray oil. Indeed many commercial spray oils perform both functions. Present day conventional petroleum spray oils are derived from light lube oil distillates.
2. Statement of the Prior Art
The prior art to which this invention relates is already aware of U.S. Pat. No. 3,097,088 which relates to plant growth regulatory compositions consisting of spray oils containing primary amine salts of 3,6 endoxohydrophthalic acid. This art is also aware of the article by R. P. Tucker (Ind. Eng. Chem., 1956, 28, 458) which showed that the aromatic hydrocarbons are not toxic to the foliage of plants in a chemical sense until they are oxidized to oil soluble asphaltogenic acids. Similarly, it should be noted that coassigned copending U.S. application Ser. No. 835,280 filed Sept. 21, 1977, discloses the elimination or reduction of phytotoxicity of petroleum spray oils by the addition thereto of from 0.01 to 8 weight percent of N,N'-di-sec. butyl-p-phenylenediamine; phenyl-a-naphthyl amine; p,p'-dioctyldiphenylamine; diphenylamine, B-naphthylamine, 2-mercaptobenzothiazole, zinc dibutyl-dithio carbamate, sulfurized sperm oil and mixtures thereof.
The horticultural spray oils used as carrier with which this invention is concerned have a minimum gravity API of 27; a viscosity at 40.degree. C. of between 8 and 20 centi-Stokes a boiling point range between about 85.degree. & 775.degree. F. and a minimum unsulfonated residue of 85%. An analysis of two typical oils used in evaluating the present invention is given in Table I.